As with turbine blades and vanes formed from more conventional superalloy materials, CMC blades and vanes are primarily equipped with internal cavities to reduce weight, reduce centrifugal load, and reduce operating temperatures of the components. These features are typically formed in CMC components using a combination of removable and expendable tooling. Internal cooling channels are advantageous for cooling both metal and CMC hot-gas path hardware as they reduce cooling flow requirements and thermal gradients/stress.
Silicon carbide (SiC)-based ceramic matrix composite (CMC) materials have been proposed as materials for certain components of gas turbine engines, such as the turbine blades, vanes, nozzles, and buckets. Various methods are known for fabricating SiC-based components, including Silicomp, melt infiltration (MI), chemical vapor infiltration (CVI), polymer inflation pyrolysis (PIP), and oxide/oxide processes. Though these fabrication techniques significantly differ from each other, each involves the use of hand lay-up and tooling or dies to produce a near-net-shape part through a process that includes the application of heat at various processing stages.
After the burn-out cycle, the CMC preform blade is very fragile due to burn-off of the volatile substances of the composite. The open tip area of the CMC preform requires capping or closing before use in gas turbines. In known processes, to close the open tip area of the CMC preform a tip cap is inserted into the fragile open tip area. The tip cap can be formed from of a CMC laminate part having a number of plies, generally 20-50 plies, and shaped as the open tip area to fill the open tip area of the CMC preform. Forming the CMC laminate tip cap by cutting out the CMC plies to the desired shape and laying up the plies in the desired geometry is time and labor intensive. Challenges also arise with placing the CMC laminate having a number of plies into the open tip area. Additionally, because both the CMC laminate and preform blade are fragile prior to densifying, these components can be easily damaged during assembly. Known techniques fail to provide robust CMC airfoil systems that suffer from the fallout of parts and significant cost. In addition, known processes suffer from desirable squeezing of the plies into the hollow cavity of the component during fabrication.